Optical waveguide

BACKGROUND

00011. Field of the Invention

0002The present invention relates to optical waveguides.

00032. Description of Related Art

0004Many modern devices incorporate optical waveguides. Generally, an optical waveguide is any structure having the ability to guide the flow of radiant energy, such as light, along a path parallel to the structure's optical axis and having the ability to contain the energy within or adjacent to the structure's surface. Examples of optical waveguides include optical fibers, light pipes, and the like. Such optical waveguides often comprise glass, acrylic, or the like.

0005<figref idref="DRAWINGS">FIG. 1A</figref> depicts an exemplary, conventional, frustoconical, optical waveguide <b>101</b>. Such frustoconical optical waveguides are used, for example, to collect light from a larger aperture and concentrate the light at a smaller aperture. Light enters optical waveguide <b>101</b> at an optical entrance <b>103</b>. If a light wave entering optical waveguide <b>101</b> at optical entrance <b>103</b> is substantially collimated, i.e., every ray of the light wave is substantially parallel to one another, and the collimated light wave is parallel to an optical axis <b>105</b> of optical waveguide <b>101</b>, substantially all of the collimated light wave exits optical waveguide <b>101</b> at an optical exit <b>107</b>. In other words, the amplitude of the light wave entering optical waveguide <b>101</b> at optical entrance <b>103</b> is substantially the same as the amplitude of the light wave exiting optical waveguide <b>101</b> at optical exit <b>107</b>.

0006For example, as shown in <figref idref="DRAWINGS">FIG. 1A</figref>, a light ray <b>109</b> of the collimated light wave enters optical waveguide <b>101</b> at optical entrance <b>103</b> and propagates substantially unattenuated through optical waveguide <b>101</b> and optical exit <b>107</b> without encountering an outer surface <b>111</b> of optical waveguide <b>101</b>. A light ray <b>113</b> of the collimated light wave enters optical waveguide <b>101</b> at optical entrance and propagates through optical waveguide <b>101</b> but encounters outer surface <b>111</b>, generally at <b>115</b>. At <b>115</b>, light ray <b>113</b> is totally, internally reflected and propagates through optical exit <b>107</b>.

0007Total internal reflection occurs when light is refracted or bent at a medium boundary enough to send it backwards, effectively reflecting the entire ray. When a light ray propagates across a boundary surface (e.g., outer surface <b>111</b>) between materials with different refractive indices, the light ray will be partially refracted at the boundary surface and partially reflected. However, if the angle of incidence (e.g., angle a) is shallower (closer to the boundary) than the critical angle, then the light ray will stop crossing the boundary altogether and, instead, totally reflect back internally within optical waveguide <b>101</b>. The critical angle is the angle of incidence wherein a light ray is refracted so that the light ray travels along the boundary between the media and is defined as:

0008<maths id="MATH-US-00001" num="00001"><math overflow="scroll"><mrow><mrow><msub><mi>θ</mi><mi>c</mi></msub><mo>=</mo><mrow><msup><mi>sin</mi><mrow><mo>-</mo><mn>1</mn></mrow></msup><mo>⁡</mo><mrow><mo>[</mo><mfrac><msub><mi>n</mi><mn>1</mn></msub><msub><mi>n</mi><mn>2</mn></msub></mfrac><mo>]</mo></mrow></mrow></mrow><mo>,</mo></mrow></math></maths><br /> wherein θ_cis the critical angle, n₁is the refractive index of the less dense material, and n₂is the refractive index of the more dense material. Total internal reflection can only occur where a light ray propagates from a denser medium to a less dense medium, i.e., from the medium with a higher refractive index to a medium with a lower refractive index. For example, total internal reflection will occur when a light ray propagates from glass to air, but not when the light ray propagates from air to glass.

0009In the example illustrated in <figref idref="DRAWINGS">FIG. 1A</figref>, as in all optical waveguides, optical waveguide <b>101</b> comprises a material having a higher refractive index than a medium <b>117</b> in which optical waveguide <b>101</b> is disposed. Since the angle of incidence a between light ray <b>113</b> and outer surface <b>111</b> is less than the critical angle for the interface or boundary between optical waveguide <b>101</b> and medium <b>117</b>, light ray <b>113</b> is totally internally reflected within optical waveguide <b>101</b>, as depicted in <figref idref="DRAWINGS">FIG. 1A</figref>, if outer surface <b>111</b> contains no optical defects. In a practical sense, however, outer surface <b>111</b> will contain optical defects and, thus, the amplitude of light ray <b>119</b> is somewhat attenuated at each encounter with outer surface <b>111</b>. Accordingly, a light ray <b>118</b> entering optical waveguide <b>101</b> will exit optical waveguide <b>101</b>, but only after encountering, and being reflected by, outer surface <b>111</b> a plurality of times. Because of the inherent optical defects in outer surface <b>111</b>, the amplitude of light ray <b>118</b> is more attenuated in optical waveguide <b>101</b> than the amplitude of light ray <b>113</b> or light ray <b>109</b>. Correspondingly, the amplitude of light ray <b>113</b> is more attenuated in optical waveguide <b>101</b> than light ray <b>109</b>.

0010Even if the light wave entering optical waveguide <b>101</b> through optical entrance <b>103</b> is not collimated light, the amplitude of the light wave exiting optical waveguide <b>101</b> through optical exit <b>107</b> may be substantially undiminished. For example, as shown in <figref idref="DRAWINGS">FIG. 1B</figref>, a light ray <b>119</b> enters optical waveguide <b>101</b> at an angle b and is refracted at an angle c at optical entrance <b>103</b> because medium <b>117</b> exhibits a lower refractive index than optical waveguide <b>101</b>. Note that, optical axis <b>105</b> is perpendicular to optical entrance <b>103</b>. Snell's law characterizes optical refraction, in that: <br /><i>n</i>₁sin(θ₁)=<i>n</i>₂sin(θ₂),<br /> wherein:

0011n₁is the refractive index of a first material (e.g., medium <b>117</b>);

0012θ₁is the angle of incidence (e.g., angle b) of a light ray in the first material (e.g., ray <b>119</b> in medium <b>117</b>);

0013n₂is the refractive index of a second material (e.g., light ray <b>119</b> in waveguide <b>101</b>); and

0014θ₂is the angle of refraction (e.g., angle c) of the light ray in the second material.

0015Light ray <b>119</b> encounters outer surface <b>111</b> of optical waveguide at angle d, generally at <b>121</b>. Because, in the illustrated example, angle d is less than the critical angle for the boundary between optical waveguide <b>101</b> and medium <b>117</b>, light ray <b>119</b> is totally internally reflected within optical waveguide <b>101</b> and exits optical waveguide <b>101</b> through optical exit <b>107</b> substantially unattenuated, except for attenuation due to optical defects in outer surface <b>111</b>.

0016At greater angles of incidence at optical entrance <b>103</b>, however, the amplitude of a light ray may be further attenuated as the light ray propagates through optical waveguide <b>101</b>. For example, as illustrated in <figref idref="DRAWINGS">FIG. 1C</figref>, a light ray <b>123</b> strikes optical entrance <b>103</b> at an angle of incidence e and is refracted at optical entrance <b>103</b> at an angle of refraction f. Light ray <b>123</b> propagates further through optical waveguide <b>101</b>, encountering outer surface <b>111</b> generally at <b>125</b> and at <b>127</b>. At <b>127</b>, however, light ray <b>123</b> strikes outer surface <b>111</b> an angle of incidence g, which exceeds the critical angle for the interface or boundary between optical waveguide <b>101</b> and medium <b>117</b>. Accordingly, light ray <b>123</b> is split, with a first portion of light ray <b>123</b> being refracted into medium <b>117</b> as light ray <b>123</b>′ and a second portion of light ray <b>123</b> being reflected in optical waveguide <b>101</b> as light ray <b>123</b>″.

0017At each successive encounter of the remaining, reflected portion of light ray <b>123</b> (e.g., light ray <b>123</b>″) with outer surface <b>111</b> of optical waveguide <b>101</b>, the remaining, reflected portion of light ray <b>123</b> is further split into a refracted component, propagating into medium <b>117</b>, and a reflected component, reflected into optical waveguide <b>101</b>. The remaining, reflected portion or component of light ray <b>123</b> is further split because the angle of incidence of the remaining, reflected portion of light ray <b>123</b> with outer surface <b>111</b> is greater than the critical angle of the interface or boundary between optical interface <b>101</b> and medium <b>117</b>. Thus, light rays having larger angles of incidence upon optical entrance <b>103</b>, such as light ray <b>123</b>, are not totally, internally reflected within optical waveguide <b>101</b> but are substantially attenuated, if not completely attenuated (as illustrated in <figref idref="DRAWINGS">FIG. 1C</figref>), as light ray <b>123</b> propagates through optical waveguide <b>101</b>.

0018As mentioned above, conventional, frustoconical, optical waveguides are often used to gather light at a larger aperture (e.g., optical entrance <b>103</b>) and focus or concentrate the gathered light at a smaller aperture (e.g., optical exit <b>107</b>). However, such optical waveguides are ineffective in applications wherein the light rays entering the larger aperture that are to be focused or concentrated at the smaller aperture are not totally, internally reflected within the optical waveguide. In some implementations, conventional, frustoconical, optical waveguides are used to concentrate or focus light onto a detector or other such electronic sensor. However, in some operational situations, the amplitude of the light exiting the optical waveguide onto the detector may be insufficient for the detector to properly operate, because a preponderance of the light rays striking the optical entrance of the optical waveguide have large angles of incidence at the optical entrance, as discussed above. In such situations, the orientation of the optical waveguide must be changed with respect to the direction at which the light rays are propagating, which may cause, for example, packaging problems. It should be noted that conventional, frustopyramidal, optical waveguides suffer from the same problems noted above with respect to conventional, frustoconical, optical waveguides.

0019While conventional, right-cylindrical, optical waveguides, such as a right-cylindrical, optical waveguide <b>201</b> of <figref idref="DRAWINGS">FIG. 2</figref>, do not generally suffer the problems described above, particular implementations of such optical waveguides do present other problems. For example, as illustrated in <figref idref="DRAWINGS">FIG. 2</figref>, optical waveguide <b>201</b> is disposed in housing <b>203</b> such that light, represented by an arrow <b>205</b>, propagates through opening <b>207</b> defined by housing <b>203</b>. Packaging constraints, however, may require optical waveguide <b>201</b> to be positioned such that an optical entrance <b>209</b> of optical waveguide <b>201</b> is not flush with housing <b>203</b>. In implementations wherein housing <b>203</b> experiences high velocity fluid flow adjacent thereto, as represented by an arrow <b>211</b>, a gap <b>213</b> between housing <b>203</b> and optical waveguide <b>201</b> may induce severe turbulence and undesirable turbulence-induced forces on housing <b>203</b>. One example of such an implementation is in airborne or waterborne vehicles, such as missiles, rockets, aircraft, drones, torpedoes, and the like.

0020While there are many designs of optical waveguides well known in the art, considerable shortcomings remain.

SUMMARY OF THE INVENTION

0021There is a need for an improved optical waveguide.

0022Therefore, it is an object of the present invention to provide a improved optical waveguide.

0023In one aspect, the present invention provides an optical waveguide, including a first end surface; a second end surface, such that the second end surface is smaller than the first end surface; and a body extending between the first end surface and the second end surface, the body defining a complexly-contoured outer surface.

0024In another aspect of the present invention, an optical waveguide is provided. The optical waveguide includes a first end surface; a second end surface, such that the second end surface is smaller than the first end surface; and a body extending between the first end surface and the second end surface, the body comprising one of a gradient-index material and a step-index material.

0025In yet another aspect, the present invention provides an optical waveguide, including a first end surface non-perpendicular with respect to an optical axis of the optical waveguide; a second end surface; and a body extending between the first end surface and the second end surface.

0026In another aspect of the present invention, a seeker assembly is provided. The seeker assembly includes a housing defining an opening and an optical waveguide disposed in the opening. The optical waveguide includes an optical entrance non-perpendicular to an optical axis of the optical waveguide; an optical exit, the optical exit being smaller than the optical entrance; and a body extending from the optical entrance to the optical exit. A detector is disposed at the optical exit of the optical waveguide.

0027The present invention provides significant advantages, including: (1) providing a means for limiting the degree of attenuation of light intensity or amplitude as the light propagates through an optical waveguide; (2) providing means for redirecting light striking an optical entrance of an optical waveguide at an orientation that is not parallel to an optical axis of the optical waveguide; (3) providing means for selectively directing certain rays of light toward an optical exit; and (4) providing means for selectively directing certain rays of light away from an optical exit.

0028Additional objectives, features and advantages will be apparent in the written description which follows.

DESCRIPTION OF THE DRAWINGS

0029The novel features believed characteristic of the invention are set forth in the appended claims. However, the invention itself, as well as, a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, in which the leftmost significant digit(s) in the reference numerals denote(s) the first figure in which the respective reference numerals appear, wherein:

0030<figref idref="DRAWINGS">FIGS. 1A-1C</figref> are stylized, side, elevational views of a conventional, frustoconical, optical waveguides illustrating their operation;

0031<figref idref="DRAWINGS">FIG. 2</figref> is a stylized representation of a conventional, right-cylindrical, optical waveguide illustrating one particular use;

0032<figref idref="DRAWINGS">FIG. 3</figref> is a stylized, side, elevational view of a first illustrative embodiment of an optical waveguide according to the present invention;

0033<figref idref="DRAWINGS">FIG. 4</figref> is a cross-sectional view of the optical waveguide of <figref idref="DRAWINGS">FIG. 3</figref> taken along the line <b>4</b>-<b>4</b> in <figref idref="DRAWINGS">FIG. 3</figref>;

0034<figref idref="DRAWINGS">FIG. 5</figref> is a cross-sectional view of second illustrative embodiment of an optical waveguide according to the present invention, alternate to the optical waveguide of <figref idref="DRAWINGS">FIG. 3</figref>;

0035<figref idref="DRAWINGS">FIG. 6</figref> is a cross-sectional view of third illustrative embodiment of an optical waveguide according to the present invention, alternate to the optical waveguide of <figref idref="DRAWINGS">FIG. 3</figref>;

0036<figref idref="DRAWINGS">FIG. 7</figref> is a stylized, side, elevational view of a fourth illustrative embodiment of an optical waveguide according to the present invention;

0037<figref idref="DRAWINGS">FIG. 8</figref> is a stylized, side, elevational view of a fifth illustrative embodiment of an optical waveguide according to the present invention;

0038<figref idref="DRAWINGS">FIG. 9</figref> is a stylized, side, elevational view of a sixth illustrative embodiment of an optical waveguide according to the present invention;

0039<figref idref="DRAWINGS">FIG. 10</figref> is a stylized, side, elevational view of a seventh illustrative embodiment of an optical waveguide according to the present invention;

0040<figref idref="DRAWINGS">FIG. 11</figref> is a cross-sectional view of a portion of the optical waveguide of <figref idref="DRAWINGS">FIG. 10</figref>, taken along the line <b>11</b>-<b>11</b> in <figref idref="DRAWINGS">FIG. 10</figref>;

0041<figref idref="DRAWINGS">FIG. 12</figref> is a stylized, side, elevational view of an eighth illustrative embodiment of an optical waveguide according to the present invention;

0042<figref idref="DRAWINGS">FIG. 13</figref> is a stylized, side, elevational view of a ninth illustrative embodiment of an optical waveguide according to the present invention;

0043<figref idref="DRAWINGS">FIG. 14</figref> is a stylized, side, elevational view of a tenth illustrative embodiment of an optical waveguide according to the present invention;

0044<figref idref="DRAWINGS">FIG. 15</figref> is a perspective view of a first illustrative embodiment of a seeker assembly according to the present invention;

0045<figref idref="DRAWINGS">FIG. 16</figref> is a stylized, top, plan view of a missile or rocket according to the present invention; and

0046<figref idref="DRAWINGS">FIG. 17</figref> is a perspective view of a second illustrative embodiment of a seeker assembly according to the present invention.

0047While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

0048Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

0049It should be noted that the following terms and phrases are intended to have a particular meaning throughout the following detailed description. The term “optical waveguide” is intended to refer to a dielectric waveguide that is capable of guiding an optical signal. A “light pipe,” which is transparent matter formed into a shape and through which light is channeled from one end to the other by total internal reflections, is one example of an optical waveguide. The term “total internal reflection” means the reflection that occurs within a substance because the angle of incidence of light striking a boundary surface is in excess of the critical angle. The term “angle of incidence” refers to the angle formed between a ray of light striking a surface and the normal to the surface at the point of incidence. A “light ray” or “ray of light” is one of the radii of a wave of light that indicates the direction of light travel.

0050Moreover, the term “critical angle” refers to the least angle of incidence at which total internal reflection takes place. The term “optically transmissive material” refers to a material that allows light to propagate therethrough. The term “index of refraction” means the ratio of the velocity of light in a vacuum to the velocity of light in a particular material for a given wavelength of light. The term “refraction” means the change in direction of a light wave due to a change in the velocity of the wave. A “surface of revolution” is a surface created by rotating a curve lying on some plane (i.e., a generatrix) around a straight line (i.e, an axis of rotation) that lies on the same plane as the curve. The term “complexly-contoured,” as it relates to surfaces or shapes, is a surface or shape that is contoured in at least two directions. A “frustum of a paraboloid of revolution” is a part of a surface having parabolic sections parallel to a single coordinate axis and elliptic sections perpendicular to that axis.

0051Yet further, an “optical entrance” is a location at which light enters a device, such as an optical waveguide. An “optical exit” is a location at which light exits a device, such as an optical waveguide. An “optical axis” is, in a refractive or reflective optical element, the straight line that is coincident with the axis of symmetry of the surfaces. The term “reflection” refers to the return of light by a surface, without change in wavelength of the light. The term “cladding” refers to one or more layers of material in intimate contact with a member, such as a body of an optical waveguide. “Vehicles” are devices, apparatuses, or the like that travel through a medium, such as air or water. Examples of vehicles include, but are not limited to, missiles, rockets, torpedoes, airplanes, helicopters, automobiles, trucks, military tanks, and drones. The term “flush” means smooth or even within manufacturing tolerances.

0052<figref idref="DRAWINGS">FIG. 3</figref> depicts a stylized representation of a first illustrative embodiment of an optical waveguide <b>301</b> according to the present invention. Optical waveguide <b>301</b> comprises a first end surface <b>303</b>, a second end surface <b>305</b>, and a body <b>307</b> extending between first end surface <b>303</b> and second end surface <b>305</b>. Optical waveguide <b>301</b> comprises an optically transmissive material having an index of refraction that is greater than an index of refraction of a medium <b>309</b> in which optical waveguide <b>301</b> is disposed. Accordingly, the material comprising optical waveguide <b>301</b> is chosen based upon at least the material of medium <b>309</b>. For implementations wherein medium <b>309</b> comprises air, optical waveguide preferably comprises glass or a polymeric material, such as acrylic.

0053In one implementation, an outer surface <b>311</b> of body <b>307</b> is a surface of revolution defined by a non-linear curve rotated about an optical axis <b>313</b> of optical waveguide <b>301</b>. In such an embodiment, a cross-section of optical waveguide <b>301</b> taken substantially perpendicular to optical axis <b>313</b> reveals outer surface <b>311</b> to be generally circular in shape, such as shown in the cross-section of <figref idref="DRAWINGS">FIG. 4</figref>. The scope of the present invention, however, is not so limited. Rather, an outer surface, corresponding to outer surface <b>311</b>, of an optical waveguide according to the present invention may be a surface of revolution defined by plurality of different curves that are each rotated partway about an optical axis, such as optical axis <b>313</b>, of the optical waveguide, such that adjacent, generated surfaces are joined. In such an embodiment, a cross-section of the optical waveguide taken substantially perpendicular to the optical axis of the optical waveguide reveals the outer surface of the optical waveguide to be non-circular in cross-section. For example, in a second illustrative embodiment of the present invention depicted in <figref idref="DRAWINGS">FIG. 5</figref>, an outer surface <b>501</b> of an optical waveguide <b>503</b> exhibits an elliptical shape. Other embodiments, however, are within the scope of the present invention. For example, in a third illustrative embodiment of the present invention, an outer surface <b>601</b> of an optical waveguide <b>603</b>, has a rectangular shape in cross-section, as illustrated in <figref idref="DRAWINGS">FIG. 6</figref>.

0054Referring again to <figref idref="DRAWINGS">FIG. 3</figref>, outer surface <b>311</b> exhibits a complexly-contoured shape. The particular shape of outer surface <b>311</b> is highly dependent upon the particular implementation of optical waveguide <b>301</b>. In one particular preferred embodiment, outer surface <b>311</b> is a frustum of a paraboloid of revolution. Other shapes, however, may be preferred in other implementations and are encompassed within the scope of the present invention.

0055One particular implementation of optical waveguide <b>301</b> is illustrated in <figref idref="DRAWINGS">FIG. 3</figref>. In this implementation, first end surface <b>303</b> serves as an optical entrance and second end surface <b>305</b> serves as an optical exit. Light rays <b>315</b>, <b>317</b> strike first end surface <b>303</b>, propagate through body <b>307</b>, and exit optical waveguide <b>301</b> through second end surface <b>305</b>. Light ray <b>315</b> strikes first end surface <b>303</b> more distal from optical axis <b>313</b> than light ray <b>317</b>; however, both light rays <b>315</b>, <b>317</b> exit second end surface <b>305</b>. Moreover, each of light rays <b>315</b>, <b>317</b> encounters outer surface <b>311</b> of body <b>307</b> only once, lessening the likelihood of attenuation of the amplitudes of light rays <b>315</b>, <b>317</b> due to optical defects in outer surface <b>311</b>. Moreover, light rays <b>315</b>, <b>317</b> encounter outer surface <b>311</b> at angles of incidence that are less than the critical angle for the interface between optical waveguide <b>301</b> and medium <b>309</b>.

0056As discussed above, the shape of the outer surface (e.g., outer surface <b>311</b>) of the optical waveguide of the present invention can be changed or “tuned” based upon the particular implementation of the optical waveguide. <figref idref="DRAWINGS">FIG. 7</figref> depicts a fourth illustrative embodiment of an optical waveguide <b>701</b> according to the present invention. As in the previous embodiment, optical waveguide <b>701</b> has an optical axis <b>703</b> and comprises a first end surface <b>705</b>, a second end surface <b>707</b>, and a body <b>709</b> extending between first end surface <b>705</b> and second end surface <b>707</b>. Body <b>709</b> defines a complexly-contoured outer surface <b>711</b> and, in this embodiment, outer surface <b>711</b> is a surface of revolution about optical axis <b>703</b>. In this particular embodiment, outer surface <b>711</b> is configured to reflect certain light rays while rejecting other light rays. In the implementation shown in <figref idref="DRAWINGS">FIG. 7</figref>, first end surface <b>705</b> serves as an optical entrance and second end surface <b>707</b> serves as an optical exit. Outer surface <b>711</b> is configured to reflect a light ray <b>713</b> toward and through second end surface <b>707</b>. However, outer surface <b>711</b> is configured to reject light ray <b>715</b>. Light ray <b>715</b> encounters outer surface <b>711</b> at an angle of incidence m that is greater than the critical angle for the interface between optical waveguide <b>711</b> and a medium <b>717</b> in which optical waveguide is disposed. Accordingly, only a fractional portion of the amplitude of light ray <b>715</b> is reflected in body <b>709</b>, but the reflected portion is not reflected toward second end surface <b>707</b>. The non-reflected portion of amplitude of light ray <b>715</b> propagates through outer surface <b>711</b> and into medium <b>717</b>. Accordingly, the optical waveguide's outer surface (e.g., outer surface <b>311</b> or <b>711</b>) can be shaped or tuned to accept desired light rays and to reject undesired light rays, based upon the light rays' angles of incidence at the optical entrance and where the light rays strike the optical entrance.

0057Generally, optical waveguides are more efficient in transmitting light when the light rays propagate parallel to the optical axis of the optical waveguide after the light rays pass through the optical entrance. This is particularly important in applications wherein a preponderance of the light propagates in generally one direction. Conventionally, the orientation of the optical waveguide is manipulated so that the maximum amplitude of light propagates substantially parallel to the optical axis of the optical waveguide. It may be impractical, or even impossible, in some potential implementations of optical waveguides to orient an optical waveguide in such a manner, for example, because of packaging constraints. The present invention, however, provides an embodiment wherein the optical entrance is canted or non-perpendicular with respect to the optical axis of the optical waveguide.

0058Accordingly, <figref idref="DRAWINGS">FIG. 8</figref> depicts a fifth illustrative embodiment of an optical waveguide <b>801</b> having an optical axis <b>803</b> and comprising a first end surface <b>805</b>, a second end surface <b>807</b>, and a body <b>809</b> extending between the first end surface <b>805</b> and the second end surface <b>807</b>. In the illustrated embodiment, first end surface <b>805</b> is canted or non-perpendicular with respect to optical axis <b>803</b> at a cant angle n, while second end surface <b>807</b> is substantially perpendicular to optical axis <b>803</b>. Other aspects of optical waveguide <b>801</b> generally correspond to the embodiment of <figref idref="DRAWINGS">FIG. 3</figref>. Cant angle n is determined, for example, based upon the direction at which desired light rays propagate with respect to optical waveguide <b>801</b> and any ancillary design constraints placed upon the location and orientation of optical waveguide <b>801</b>. Specifically, cant angle n is proportional to an angle p between the direction at which the desired light is propagating and optical axis <b>803</b>. In other words, as angle p increases, so does cant angle n.

0059In one particular implementation, as shown in <figref idref="DRAWINGS">FIG. 8</figref>, first end surface <b>805</b> serves as an optical entrance and second end surface <b>807</b> serves as an optical exit. First end surface <b>805</b> is canted or non-perpendicular with respect to optical axis <b>803</b> at cant angle n, such that a light ray <b>811</b>, striking first end surface <b>805</b> at angle p with respect to optical axis <b>803</b>, is refracted at first end surface <b>805</b> into optical waveguide <b>801</b> along a path substantially parallel to optical axis <b>803</b>. In some applications, it may be desirable for light rays to be refracted such that the light rays propagate in a direction within optical waveguide <b>801</b> other than parallel to optical axis <b>803</b>. In such applications, cant angle n is altered to produce the desired propagation path. Embodiments other than the particular construction illustrated in <figref idref="DRAWINGS">FIG. 8</figref> are within the scope of the present invention.

0060Moreover, the scope of the present invention encompasses a generally frustoconical, optical waveguide having a canted end surface. Accordingly, a sixth illustrative embodiment of the present invention is depicted in <figref idref="DRAWINGS">FIG. 9</figref>, wherein an optical waveguide <b>901</b> has an optical axis <b>903</b> and comprises a first end surface <b>905</b>, a second end surface <b>907</b>, and a frustoconical body <b>909</b> extending between first end surface <b>905</b> and second end surface <b>907</b>. First end surface <b>905</b> is canted or non-perpendicular with respect to optical axis <b>903</b>. Conventional, frustoconical, optical waveguides have end surfaces that are substantially perpendicular to optical axes of the waveguides. Optical waveguide <b>901</b> of the present invention, however, has improved optical transmission properties over conventional, frustoconical, optical waveguides due to canted first end surface <b>905</b> and allows optical waveguide <b>901</b> to be oriented such that light rays striking first end surface <b>905</b>, propagating in a direction that is non-parallel with respect to optical axis <b>903</b>, are refracted at first end surface <b>805</b> into optical waveguide <b>901</b> along paths substantially parallel to optical axis <b>903</b>.

0061In some applications, it is desirable to only allow light waves of a certain wavelength or light waves within a certain range of wavelengths to fully propagate through an optical waveguide. Accordingly, <figref idref="DRAWINGS">FIG. 10</figref> depicts a seventh illustrative embodiment of an optical waveguide <b>1001</b> according to the present invention. In this embodiment, optical waveguide <b>1001</b> has an optical axis <b>1003</b> and comprises a first end surface <b>1005</b> and a second end surface <b>1007</b>. Optical waveguide <b>901</b> further comprises a first body portion <b>1009</b>, extending between first end surface <b>1005</b> and a first intermediate surface <b>1011</b>, and a second body portion <b>1013</b>, extending between second end surface <b>1007</b> and a second intermediate surface <b>1015</b>. An optical filter <b>1017</b> is disposed between first intermediate surface <b>1011</b> and second intermediate surface <b>1015</b>. Generally, optical filters selectively allow light having certain properties, such as a particular range of wavelengths, to propagate therethrough. Preferably, optical filter <b>1017</b> is disposed as close to an optical entrance (e.g., first end surface <b>1005</b>) of optical waveguide <b>1001</b> as practical. The selection of filter <b>1017</b> is highly implementation specific. In various embodiments, filter <b>1017</b> may comprise an absorptive filter, a reflective filter, a monochromatic filter, an infrared filter, an ultraviolet filter, a neutral density filter, a longpass filter, a shortpass filter, a bandpass filter, a polarization filter, or the like.

0062In one embodiment, an optical grease is disposed between optical filter <b>1017</b> and first intermediate surface <b>1011</b> and between optical filter <b>1017</b> and/or second intermediate surface <b>1015</b> to minimize undesirable optical aberrations. Optical filter <b>1017</b>, however, may be rigidly attached to first intermediate surface <b>1011</b> and/or second intermediate surface <b>1015</b> or may be integral with first intermediate surface <b>1011</b> and/or second intermediate surface <b>1015</b>.

0063Any of the embodiments of the present invention may include absorptive or reflective cladding, or may omit such cladding. For example, in an eighth illustrative embodiment of the present invention, optical waveguide <b>1001</b> of <figref idref="DRAWINGS">FIG. 10</figref> includes a cladding layer <b>1101</b> disposed on an outer surface <b>1103</b> of second body portion <b>1013</b>, as shown in <figref idref="DRAWINGS">FIG. 11</figref>. It should be noted that, in embodiments including reflective cladding, light rays that would otherwise exit through outer surfaces of the optical waveguide will be reflected back into the optical waveguide and through the optical entrance. Moreover, it should be noted that the outer surfaces (e.g., outer surfaces <b>311</b>, <b>711</b>, and the like) of the optical waveguides in any of the embodiments of the present invention may include ridge or dimple features to affect the reflective characteristics of the outer surfaces.

0064A canted end surface may also be applied to generally right-cylindrical optical waveguides and such optical waveguides are encompassed by the scope of the present invention. For example, in a ninth illustrative embodiment of the present invention, a generally right-cylindrical optical waveguide <b>1201</b> is depicted in <figref idref="DRAWINGS">FIG. 12</figref>. Optical waveguide <b>1201</b> includes an optical axis <b>1203</b> and comprises a first end surface <b>1205</b> that is canted or non-perpendicular with respect to optical axis <b>1203</b>. In the illustrated embodiment, optical waveguide <b>1201</b> further comprises a second end surface <b>1207</b> that is substantially perpendicular to optical axis <b>1203</b>. Optical waveguide <b>1201</b> includes a filter <b>1209</b>, generally corresponding to filter <b>1017</b> of <figref idref="DRAWINGS">FIG. 10</figref>, which may be omitted in other embodiments.

0065<figref idref="DRAWINGS">FIG. 13</figref> depicts a tenth illustrative embodiment of an optical waveguide <b>1301</b> according to the present invention. In this embodiment, optical waveguide <b>1301</b> is generally frustoconical in shape and comprises a first end surface <b>1303</b>, a second end surface <b>1305</b>, and a body <b>1307</b> extending between first end surface <b>1303</b> and second end surface <b>1305</b>. However, body <b>1307</b> comprises a gradient-index (GRIN) or step-index material that exhibits a progressively higher refractive index proportional to a radial distance from an optical axis <b>1309</b> of the optical waveguide <b>1301</b>. In the illustrated embodiment, the refractive index of body <b>1307</b> increases in the directions indicated by a double-headed arrow <b>1311</b>. For example, the refractive index of body <b>1307</b> at <b>1313</b> is greater than at <b>1315</b>. Accordingly, a light ray <b>1317</b> entering optical waveguide <b>1301</b> at first end surface <b>1305</b> is refracted to a greater degree as light ray <b>1317</b> propagates toward second end surface <b>1307</b> than a light ray <b>1319</b>.

0066While first end surface <b>1303</b> of optical waveguide <b>1301</b> is illustrated as being substantially perpendicular to optical axis <b>1309</b>, the scope of the present invention is not so limited. Rather, in an eleventh illustrative embodiment of the present invention depicted in <figref idref="DRAWINGS">FIG. 14</figref>, an optical waveguide <b>1401</b> comprising a GRIN or step-index material comprises a first end surface <b>1403</b> that is canted or non-perpendicular with respect to an optical axis <b>1405</b> of optical waveguide <b>1401</b>. As in the embodiment of <figref idref="DRAWINGS">FIG. 13</figref>, the refractive index of optical waveguide <b>1401</b> increases in the directions indicated by a double-headed arrow <b>1407</b>. In the particular implementation shown in <figref idref="DRAWINGS">FIG. 14</figref>, a light ray <b>1409</b> enters optical waveguide <b>1401</b> at first end surface <b>1403</b>, which serves as an optical entrance. Immediately within a body <b>1411</b> of optical waveguide <b>1401</b>, light ray <b>1409</b> propagates substantially parallel to optical axis <b>1405</b>. However, the GRIN or step-index material of body <b>1411</b> refracts light ray <b>1409</b> toward optical axis <b>1405</b> and a second end surface <b>1413</b> of optical waveguide <b>1401</b>.

0067It should be noted that, while the first end surfaces (e.g., first end surfaces <b>303</b>, <b>705</b>, <b>805</b>, <b>905</b>, <b>1005</b>, <b>1205</b>, <b>1303</b>, and <b>1403</b>) are discussed herein as serving as optical entrances and the second end surfaces (e.g., second end surfaces <b>305</b>, <b>707</b>, <b>807</b>, <b>907</b>, <b>1007</b>, <b>1207</b>, <b>1305</b>, and <b>1413</b>), the scope of the present invention is not so limited. Rather, in some applications, the second end surfaces will serve as optical entrances and the first end surfaces will serve as optical exits.

0068<figref idref="DRAWINGS">FIG. 15</figref> depicts a first illustrative application for the optical waveguide of the present invention. In this particular embodiment, a seeker assembly <b>1501</b> of a guidance system for a missile or rocket, such as the illustrative embodiment of a missile or rocket <b>1601</b> according to the present invention depicted in <figref idref="DRAWINGS">FIG. 16</figref>, comprises a housing <b>1503</b> defining a plurality of openings <b>1505</b> in which a corresponding plurality of optical waveguides <b>1507</b> are disposed. Such a seeker assembly may be adapted for use in other types of vehicles, however, and such seeker assemblies and vehicles are within the scope of the present invention. While the illustrated embodiment provides four openings <b>1505</b> and four optical waveguides <b>1507</b>, the scope of the present invention is not so limited. Rather, the scope of the present invention encompasses a seeker assembly incorporating any suitable number of openings <b>1505</b> and optical waveguides <b>1507</b>, for example, one or more openings <b>1505</b> and a corresponding one or more optical waveguides <b>1507</b>.

0069In the illustrated embodiment, each optical waveguide <b>1507</b> extends to a detector <b>1509</b>, which detects light waves that have propagated optical waveguide <b>1507</b> attached thereto. Alternatively, a plurality of optical waveguides <b>1507</b> may be optically coupled to a single detector <b>1509</b>. First end surfaces <b>1511</b> of optical waveguides <b>1507</b> serve as optical entrances and are substantially flush with an outer surface <b>1513</b> of housing <b>1503</b>. In some embodiments, housing <b>1503</b> may comprise a radome or a portion of a radome. The present invention allows non-hemispherical radomes, such as radomes having conic-like shapes, to be utilized. Moreover, the use of an optical waveguide according to the present invention allows a central volume, generally at <b>1514</b>, to be available for other components of the missile or rocket. While optical waveguides <b>1507</b> may comprise any embodiment of an optical waveguide according to the present invention, optical waveguides <b>1507</b> preferably have a construction corresponding to the embodiment of <figref idref="DRAWINGS">FIG. 8</figref>, <figref idref="DRAWINGS">FIG. 9</figref>, or <figref idref="DRAWINGS">FIG. 14</figref>.

0070In some embodiments, outer surfaces (e.g., outer surfaces <b>311</b>, <b>711</b>, <b>1103</b>, or the like) of optical waveguides <b>1507</b> are complexly-contoured. In such embodiments, the shape of the outer surface is configured to allow light rays, such as light ray <b>1515</b> propagating in a particular direction or within a range of directions to propagate through optical waveguides <b>1507</b>. For example, the outer surfaces of optical waveguides <b>1507</b> may be configured or tuned to allow light rays propagating generally parallel with a boresight axis <b>1517</b> of seeker assembly <b>1501</b> to propagate through optical waveguides <b>1507</b> to detectors <b>1509</b>. In other embodiments, however, the outer surfaces optical waveguides <b>1507</b> may be configured or tuned to allow light rays propagating in directions other than parallel to boresight axis <b>1517</b> to propagate through optical waveguides <b>1507</b> to detectors <b>1509</b>.

0071Alternatively, optical waveguides <b>1507</b> may comprise GRIN or step-index materials that are configured or tuned to allow light rays propagating generally parallel with a boresight axis <b>1517</b> of seeker assembly <b>1501</b> to propagate through optical waveguides <b>1507</b> to detectors <b>1509</b>. In other embodiments, however, the GRIN or step-index materials of optical waveguides <b>1507</b> may be configured or tuned to allow light rays propagating in directions other than parallel to boresight axis <b>1517</b> to propagate through optical waveguides <b>1507</b> to detectors <b>1509</b>.

0072It should be noted that the present invention does not require all of optical waveguides <b>1507</b> to have the same configuration. For example, some of optical waveguides <b>1507</b> may be configured or tuned to allow light rays propagating substantially parallel with boresight axis <b>1517</b> to propagate therethrough, while other optical waveguides are configured or tuned to allow light rays propagating in other directions to propagate therethrough. Moreover, some optical waveguides <b>1507</b> may have complexly-contoured outer surfaces while others comprise GRIN or step-index materials. Any suitable combination of embodiments of the present invention may be used as optical waveguides <b>1507</b>.

0073While <figref idref="DRAWINGS">FIG. 15</figref> illustrates optical waveguides <b>1507</b> being generally symmetrically, radially disposed about housing <b>1503</b>, the scope of the present invention is not so limited. Other configurations are possible and within the scope of the present invention. For example, <figref idref="DRAWINGS">FIG. 17</figref> depicts an alternative, illustrative embodiment of a seeker assembly <b>1701</b> wherein optical waveguides <b>1703</b> are both radially and axially disposed about a housing <b>1705</b>. Note that optical waveguides <b>1703</b> may comprise any embodiment of an optical waveguide according to the present invention, optical waveguides <b>1703</b> preferably have a construction corresponding to the embodiment of <figref idref="DRAWINGS">FIG. 8</figref>, <figref idref="DRAWINGS">FIG. 9</figref>, or <figref idref="DRAWINGS">FIG. 14</figref>. It should also be noted that light exiting from optical adjacent optical waveguides <b>1703</b> may be optically coupled to a single detector <b>1509</b>, as illustrated in <figref idref="DRAWINGS">FIG. 17</figref>, or the light from each individual optical waveguide <b>1703</b> may be coupled to corresponding, individual detectors <b>1509</b>.

0074The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below. It is apparent that an invention with significant advantages has been described and illustrated. Although the present invention is shown in a limited number of forms, it is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof.